Dental jacket crown, coping and method of construction

ABSTRACT

The dental jacket crown of the present invention is prepared from a thin metal foil substrate which is coated with a noble based metal composition having a low fusing temperature and folded in a predetermined manner to form multiple folds in the form of triangular like flaps or pleats. The folded foil represents the coping of the present invention. The coping is mounted over a die of the prepared tooth and the flaps wrapped in overlapping formation and then adapted to the die. The die is removed and the structure heated preferably under a bunsen burner. A bonding material may be coated over the free standing structure if desired. A veneering material such as porcelain is then coated over the structure to form the crown.

This is a continuation in part of Application Ser. No. 414,415 filedSept. 2, 1982, now U.S. Pat. No. 4,459,112, issued July 10, 1984.

This invention relates to the field of dental restorations and moreparticularly to the jacket crown restoration, a jacket crown coping fora jacket crown restoration and to a method for forming a jacket crown.

Dental porcelain, a conventional material composed of a mixture offeldspar, quartz and kaolin is commonly used in fabricating dentalrestorations. The most prevalent crown construction for dentalrestorations is the porcelain veneer cast metal crown. The cast metalcrown is fabricated using a relatively thick metal understructure formedfrom casting an investment of a wax or plastic pattern of the preparedtooth. Dental porcelain is then applied in layers over part or all ofthe understructure and fired at high temperature to form a veneer. Themetal understructure is preferably formed from a noble based metal oralloy predominantly of gold. The thickness of the cast metalunderstructure ranges from typically 0.3 to 0.5 mm. The cast metalunderstructure is expensive and particularly so for a noble based metalunderstructure. The weight of a precious metal cast crown is from one tothree grams. Since the bulk of the restoration is no greater than thatof the tooth structure which originally occupied the space, the use of athick metal understructure minimizes the permissible thickness for thetranslucent porcelain veneer. Moreover, exposure of the metalunderstructure will detract from the esthetics of the restoration.

It is well known that the full porcelain or porcelain jacket crown isesthetically superior to all other crown restorations and is virtuallyimpossible to visually distinguish from a natural tooth. Accordingly, itshould be commonplace but is, in general, indicated for use only as afull coverage for an anterior tooth where esthetics is the primeconsideration. The limited use of the porcelain jacket crown isattributable to its present method of construction with the strength ofthe jacket crown dependent upon the strength of the porcelain materialcomposition. Porcelain is inherently structurally weak and fragile. Inaddition, the present day method of construction requires a high degreeof proficiency to establish accurate marginal fit and finish and toavoid poor seating of the crown occlusally relative to the preparation.An improper fit at the gingival margin results in a cement line whichreadily washes away inviting decay and loosening the crown attachment.

In the conventional process for preparing a porcelain jacket crown aplatinum foil is swaged about the prepared die of the tooth to form amolded substrate upon which the procelain may be fired. The foil is thenremoved from the substrate before the crown is cemented to the toothpreparation. The latter requirement is considered a principle failing ofthe conventional porcelain jacket crown preparation. An improvedporcelain jacket crown construction in which the swaged foil substrateis itself included as an integral component of the finished porcelainjacket crown is taught and decribed in U.S. Pat. No. 4,273,580 issued tothe Applicants herein, the disclosure of which is herein incorporated byreference. In the latter patent the metal foil substrate forms the coreof the jacket crown. A coating of a predetermined noble based metalcomposition is sintered to the foil substrate which is then adapted tothe die in a manner similar to that in the conventional preparation of aporcelain jacket crown. Although this jacket crown construction willexhibit substantially improved physical properties, its method ofconstruction is still dependent upon the skill and dexterity of asuperior dental technician.

The present invention utilizes an entirely new technique forconstructing a porcelain jacket crown which overcomes all of theshortcomings of the conventional porcelain jacket crown in mechanicalproperties, construction and preparation. In fact the preformed copingof the present invention is readily adaptable by a technical novicewithout any special skills. Use of the preformed coping in accordancewith the present invention simplifies construction of a porcelain jacketcrown and significantly contributes to uniformity in result without thedependency on the skill of the dental technician.

The porcelain jacket crown of the present invention may be prepared morequickly and more accurately relative to conventional methods ofpreparation. Moreover, the dental laboratory does not have to wax,invest, cast or polish the final metal structure as is done in making aporcelain veneer cast metal crown.

In addition, the present invention may be used with any conventionaltooth margin preparations such as: chamfer, shoulder, chamfer bevel,shoulder bevel, knife edge and feather edge. The margin may also bereinforced if desired. The porcelain jacket crown prepared in accordancewith the present invention will have an almost invisible metal line atthe gingiva. An even further distinct advantage of the present inventionlies in the reduction in the weight of the metal in a jacket crown ofthe present invention which is only 200 to 300 milligrams.

Accordingly, it is the principle object of the present invention toprovide a porcelain jacket crown having a high resistance to fracturecomparable with or even greater than the conventional porcelain veneercast metal crown.

Another object of the present invention is to provide a preformed copingfor forming the porcelain jacket crown of the present invention.

An even further object of the present invention is to provide a methodfor constructing a jacket crown.

Further objects and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread in conjunction with the accompanying drawings of which:

FIG. 1 is an enlarged perspective of a segment of the preferred metalfoil starting material of the present invention in its preferredcircular geometry;

FIG. 2 is a perspective of a dental coping prepared in accordance withthe present invention from the metal foil starting material of FIG. 1;

FIG. 3 is a transparency in perspective of the dental coping of FIG. 2in the initial stage of being molded to a die of the prepared tooth;

FIG. 4 is another transparency in perspective of the dental coping inFIG. 3 in its final stages of being adapted to the die of the preparedtooth; and

FIG. 5 is an illustration in perspective of the dental coping of FIG. 3as a free standing structure after having been adapted to the die.

Referring now to FIG. 1 in which a metal foil segment 10 is shownrepresenting the starting material for preparing the jacket crown inaccordance with the present invention. The metal foil segment 10 ispreferably circular in geometry and composed of a thin foil metalsubstrate 12 preferably of platinum or another high fusing temperaturemetal or metal alloy and a thin coated layer 14 superimposed on the foilmetal substrate 12. The coated layer 14 should be of a noble metal basedcomposition preferably with gold as its major constituent or of puregold. There are numerous gold based compositions known to those skilledin the dental arts for use in the preparation of a dental restorationand upon which a veneering material such as porcelain may be fired. Thepreferred composition of the coated layer 14 should have a relativelylow melting temperature characteristic and contain at least 50% goldwith one or more of the following elements in combination: silver,palladium, platinum, iridium, copper and aluminum. A conventional bindermay be added to the composition so that it may spread more readily overthe platinum foil substrate 12 to form the coated layer 14. The coatedlayer 14 should form a bonded matrix with or without the application ofheat which has the physical properties of being flexible and malleable.The gold based composition should have a low temperature fusingcharacteristic such that it flows after sufficient heat is applied forreasons which will be explained in greater detail hereafter.

The thickness of the foil substrate 12 should be in the range of between15 to 50 microns with an optimum thickness of 25 to 27 microns. Thethickness of the gold based layer 14 should be between 10 to 50 micronsand preferably between 15 to 25 microns.

The metal foil segment 10 is preferably round although any geometry maybe used in which multiple folds may be made which will partially overlapone another when adapted to a die as hereafter explained. When the metalfoil segment 10 is circular its diameter for a typical die is betweenabout 18 to 28 mm.

The metal foil segment 10 of FIG. 1 is folded into a predeterminedgeometrical shape having a multiple number of fold lines 18 as shown inFIG. 2 for forming the dental coping 16 of the present invention. Themultiple fold lines 18 may be formed by hand or by machine. Thetechnique or mechanism employed to perform the folding operation is notcritical to the present invention. It is the arrangement of multiplefold lines in a predetermined array to form multiple flaps or pleatswhich forms the underlying theory in the preparation of a jacket crownin accordance with the present invention.

An example of a hand folding operation that may be used for forming apreferred arrangement of fold lines 18 from the metal foil segment 10involves placing the metal foil segment 10 over one end of a cylindricalsupport bar (not shown) and squeezing the segment 10 into fold lines 18using the thumb and forefinger of one hand while holding the segment 10in place over the support bar. In such case each fold line 18 willradially extend from a central unfolded area 20. The central unfoldedarea 20 will conform in dimension to the support bar upon which it wasplaced in forming the fold lines 18. The diameter of the unfolded areais not significant provided it is small relative to the total area ofthe segment 10.

Another hand folding operation simply involves folding the segment 10 inhalf and then in quarters until the desired number of fold lines 18 areformed. This is a somewhat less desirable procedure since the fold lineswill extend radially from a central point or apex without forming anunfolded area 20 in the center of the segment 10. It should however beunderstood that forming an unfolded area 20 is not critical to theinvention.

The multiple folds form substantially triangular like pleats or flaps 22with a curved base line 24 shown as a straight line in FIGS. 2 and 3 forsimplicity. Each triangular like flap 22 has two fold lines 18 with acommon fold line 18 between adjacent pairs. The number of flaps 22 thatshould be formed may vary with four to sixteen being preferred and witheight being the optimum number for most typical jacket crownpreparations.

The preferred geometry of the dental coping 16 includes a multiplenumber of fold lines 18 which radially extend from a centrally locatedunfolded area 20 in an arrangement which form triangular-like flaps 22.The dental coping 16 should preferaly be modified to include a pluralityof small slotted openings 26. These openings 26 may be made as anintegral part of the manufacturing operation of the dental coping 16 oras part of the procedure of the dental technician in the preparation ofthe jacket crown as will hereinafter be explained in greater detail. Theslotted openings 26 are slits formed in the segment 10 preferably alongthe fold lines 18. Neither the position of the slotted openings 26,their size or number are critical. Their primary function is to provideaccess for the noble metal composition to flow to the underside oruncoated surface of the platinum foil substrate 12 when heat is appliedto the finished coping 16 during the final preparatory step in thepreparation of a jacket crown.

FIGS. 3-6 illustrate the preferred sequence of steps in the preparationof a jacket crown in accordance with the present invention. Thepreformed coping 16 is placed over a die 28 of a prepared tooth with theunfolded area 20 seated upon the top or occlusal end 29 of the die 28.The die 28 is conventionally prepared from an impression of the preparedtooth and is a replica thereof. The unfolded area 20 facilitatescentering the dental coping 16 over the die 28 and makes the coping 16easier to adapt to the die 28 as is more readily apparent from FIG. 4.

Each of the flaps 22 are wrapped tightly around the die 28 in a uniformclockwise or counter clockwise oriented sequence resulting preferably inan arrangement of overlapping or partially overlapping flaps 22 as shownin FIG. 4. The coping 16 should also extend over the gingival margin 31.The die 28 and coping 16 is then placed in a swaging device (not shown)or pressure is applied by hand to adapt it to the die 28. The coping 16is then removed from the die leaving a free standing structure 33 asshown in FIG. 5. Heat is then applied to the free standing structure 33by placing it over the flame of a bunsen burner for between five tothirty seconds based on flame temperature until the structure 33 getscherry red and shiny. Alternatively the free standing structure 33 canbe placed in a furnace and sintered at a temperature of about 1020° to1070° C. until the same result is achieved. The low fusing preferablygold based composition of the metal layer 14 will flow through theslotted openings 26 to form a compact matrix between the foil substrate12 and the gold based composition on the underside thereof without anyair pockets.

After the heating step, porcelain can be directly applied in aconventional manner to form the jacket crown of the invention. It ishowever desirable but not essential, to coat the outside surface of thefree standing foil structure 33 using a bonding composition to achievean unbreakable bond between the porcelain layers and the foil structure33. A preferred bonding composition is disclosed in a copending U.S.Patent Application Ser. No. 171,255 entitled Bonding Material and MethodFor Bonding A Ceramic To A Nobel Based Metal, now abandoned, thedisclosure of which is herein incorporated by reference. The bondingmaterial disclosed in this application includes a nobel based metalcomposition in combination with a halide of a noble metal preferably anoble metal halide. The bonding material must be sintered to the foilstructure 33 at a temperature above 1600° F. This can be achievedsimultaneously with the firing of the required porcelain outer layers.Any number of porcelain layers may be applied and fired for forming thejacket crown of the invention. Generally, three or more layers ofvarying dental porcelain composition starting with an opaque layer arebuilt up and fired at temperatures in a range from about 1600° to 1820°F. Before firing the final glaze the area below the gingival margin iscut and the porcelain shaped and finished to the correct gingival marginfor the prepared tooth.

After the final glaze the crown is ready to be inserted into the mouthand cemented to the tooth using any conventional dental cementcomposition. It is suggested practice to roughen the interior of thecrown i.e. the unerside of the inner substrate layer 12 before the crownis cemented to the tooth. The roughness may be achieved by sandblasting.

Although the invention was described in connection with the applicationof porcelain for forming a porcelain jacket crown it is equallyapplicable to the use of any polymer veneering material such asconventional dental acrylics in substitution of the porcelain ceramicmaterial for the superstructure of the jacket crown.

It is to be understood that although the invention has been described inaccordance with the preferred embodiment in which the multiple foldsform fold lines 18 extending radially from the apex or top area 20 ofthe thin foil substrate it is equally within the concept of the presentinvention to have the multiple folds arranged circumferentially around acentral axis extending vertically through the central area 20 of thethin foil substrate 10. In the latter case the multiple folds are foldedover the substrate preferably in an overlapping or partially overlappingrelationship by pressing one fold over another in a telescoping fashion.

What we claim is:
 1. A jacket crown comprising a composite bodyincluding a thin foil of high fusing temperature metal substantially ofplatinum having a surface geometry conforming to a die to which it hasbeen adapted with the foil having a minimum of at least three foldedover pleats in a substantial symmetrical arrangement around the body ofthe foil with each pleat forming a triangular like flap in the unfoldedposition and wherein said foil has an unfolded area substantially in thecenter of the foil body with said foil having at least one thin coatedlayer of a gold based noble metal composition of up to 100% goldsuperimposed over one surface of said thin foil and disposed beneath thefolded over pleats and a relatively thick outer coating of a dentalveneering material.
 2. A jacket crown as defined in claim 1 wherein eachof the folds is arranged substantially circumferentially around acentral axis extending vertically through said unfolded area in thecenter of the foil body.
 3. A jacket crown as defined in claim 2 whereinsaid gold based noble metal composition comprises substantially gold andat least one of the following elements selected from the groupconsisting of: silver, palladium, iridium, copper and aluminum.
 4. Ajacket crown as defined in claim 1 wherein said folded over pleatsoverlap one another.
 5. A dental coping for a jacket crown restorationcomprising a thin foil of high fusing temperature metal arranged in aprefolded geometrical configuration with an unfolded central areawherein the prefolded geometry includes a minimum of at least threepleated sections substantially symmetrically disposed around the centralarea with each pleated section represented by fold lines which form atriangular like flap and at least one coated layer of a gold based noblemetal composition of up to 100% gold superimposed upon the surface ofsaid thin foil and disposed beneath the folded over pleats.
 6. A dentalcoping for a jacket crown as defined in claim 5 wherein said pleatedsections are arranged substantially circumferentially around a centralaxis extending through said unfolded area in the center of the foilbody.
 7. A dental coping as defined in claim 5 wherein said folded overpleats overlap one another.
 8. A method of forming a dental jacket crowncomprising the steps of:preparing a thin metal foil of high fusingtemperature metal into a substantially circular substrate; coating onesurface of the foil substrate with at least one layer of a gold basednoble metal composition of up to 100% gold with a lower fusingtemperature than that of the metal foil substrate; forming at leastthree pleats in said coated foil substrate around an unfolded areadisposed substantially in the center of the circular foil; mounting saidcoated foil substrate over a die of the prepared tooth with the coatedsurface exposed and with the unfolded area above the occlusal end of thedie; adapting said foil to said die; removing said die for providing aninner structure for said jacket crown; heating said inner structureabove the low fusing temperature of said noble based gold composition;and coating a fired on porcelain veneering material over said innerstructure.
 9. A method as defined in claim 8 wherein said pleats arearranged substantially circumferentially around a central axis extendingvertically through said unfolded area in the center of the foil.
 10. Amethod as defined in claim 8 wherein each pleat is of a size such thatupon folding it will overlap an adjacent pleat.